Much of the following also applies to monitors that are not displaying color correctly. The monitor problem may or not be the network/DSL installation. Computers often (and purposely go out of their way) to confuse humans into thinking two coincidental events are related. And humans have a way of breaking things while fixing other things. Larry
Q. How do I troubleshoot a monitor that occasionally goes blank (black, no cursor) or will not always come on when I turn on my computer?
A. Look for bent pins in the monitor plug that connects to the computer. Check for loose power plug. I use a tweaker (small screw driver) to straighten them. Be very careful; they can break easily, depending on the monitor. Check the monitor cable to be sure it is fully plugged-in and make sure it is screwed down. Wiggle it at both ends to see if the cable is defective. I also give the monitor a "technicianís whack" with my hand to see if there is something loose in it, but a technicianís whack can only be learned after many years of experience.
A frequent monitor problem is the failure of the green function which is usually controlled by a relay, which can often be heard clicking in an out when it or the supporting circuitry is defective. Most green monitors also have an LED, which will turn green when they are online (receiving a signal/video from the computer; display is visible) and amber or another color when they are not. Some will display "No Signal" or something similar when they are on and are not detecting a signal from the computer. Often, one can get the monitor back on line by repeatedly pushing the power-on switch or holding it in for a while (still another art).
The problem could be in the computer. Reseat the video board. If you have an AGP display adapter, remove any expansion boards in the PCI slot next to the AGP slot. That PCI slot usually shares an interrupt (http://duxcw.com/faq/irq/irq.htm) with the AGP slot. Try another monitor to determine if the problem is in the computer or the monitor itself. Try another display adapter.
Check the display adapter, motherboard (, and monitor manufacturer's web sites for known issues and solutions thereto.
The monitor may need the attention of a qualified technician in a shop equipped to troubleshoot and repair the monitor. The availability of parts and authorization by the monitor manufacturer are considerations that should be explored. The solvency and reputation of the firm doing the repairs should be checked if possible. Obtain a firm figure in writing for the cost of providing an estimate for repairs and an understanding of the shop's policies before making any commitments/payments.
Before taking/shipping the monitor to a computer shop/repair depot, one should try determine if repairs are warranted based on the age of the monitor and the replacement cost. Many shops charge a flat fee to repair a monitor. The fee may not include cathode ray tube (picture tube; CRT) or other parts. If the fee plus shipping is more than half the cost of new monitor, the monitor is more than likely not worth fixing, if it is more than a couple of years old. The decision, to repair or replace a monitor, is of course, up to you.
Warning! Monitors have very high voltages inside the case and are extremely dangerous. Do not take a monitor apart unless you are qualified to do so. Dangerous (life threatening) shocks are possible even if the power cord is disconnected. The cathode ray tube is also dangerous and can implode causing injury or death. If you do take a monitor apart or handle a monitor, you do so at your own risk.